Interaction Mechanisms and Grinding-Force Behavior in Ultrasonic-Assisted High-Shear and Low-Pressure Grinding of LN Using Ball-End Body-Armor-like Abrasive Tools

Lithium niobate crystals are typical soft-brittle optoelectronic materials widely used in optical modulation, communication, sensing, and precision optical devices. However, conventional grinding easily induces surface scratches, particle embedding, subsurface cracks, and severe processing damage, which restricts high-precision, low-damage manufacturing. To solve this problem, ultrasonic-assisted high-shear and low-pressure grinding (HSLPG) with ball-end body-armor-like abrasive tools (BAAT) was proposed. Considering the high-frequency, intermittent contact characteristics induced by ultrasonic vibration, the vector superposition of the ultrasonic tangential impact load and the normal external load was introduced. Based on ultrasonic vibration kinematics, elastohydrodynamic lubrication and Hertz contact theory, a theoretical grinding force prediction model for ultrasonic-assisted HSLPG was established. The spatial distribution characteristics of elastohydrodynamic pressure under different ultrasonic frequencies, amplitudes, normal loads and spindle rotational speeds were revealed, and the intrinsic regulation mechanism of process parameters on contact pressure and tangential grinding force was clarified. Single-factor grinding experiments on a lithium niobate crystal were conducted to verify the accuracy of the proposed model. The results show that the predicted grinding force values are in good agreement with the experimental values, with an average error of only 5.04%. Increasing the ultrasonic frequency and amplitude reduces the average tangential grinding force, whereas increasing the normal load and spindle speed significantly increases the grinding force. Compared the tangential grinding forces of conventional grinding and ultrasonic-assisted HSLPG.